In fluid systems utilizing pressurized fluids, such as high-temperature gaseous fluids, it is common practice to include one or more blow-down safety valves which are placed at predetermined locations in the system for the purpose of preventing the pressure of the fluid in the system from exceeding a predetermined maximum limit. These safety valves generally include an inlet conduit communicating with the fluid system and forming a valve seat, and a valve member biased into a seated position by a spring or the like that is preset to permit the normally seated valve member to move to an open positon when the pressure in the fluid system, acting against the valve member, reaches a predetermined maximum limit, thereby relieving the pressure in the fluid system to prevent such pressure from exceeding the predetermined maximum limit. A typical blow-down safety valve of this sort is disclosed in co-pending U.S. Application Ser. No. 521,975,filed Nov. 8, 1974.
It is recognized that as the system pressure approaches this predetermined maximum limit, the opposite forces (e.g. the spring and the fluid pressure) acting against the valve member approach a balance, and the valve member then has a tendency to permit excessive bleeding at the valve seat, which, in some instances, may begin prior to the system pressure reaching the aforesaid maximum pressure limit. This excessive and/or premature bleeding can cause irregular operation of the valve and may result in the system pressure exceeding its predetermined maximum pressure limit without the valve member opening to its fully opened position.
Accordingly, it is highly desirable in blow-down safety valves of the type in question to have the valve member open sharply and fully when the predetermined maximum pressure is reached in the fluid system, and eliminate or reduce the aforementioned tendency of the valve member to permit excessive bleeding of the fluid when such maximum pressure is approached. Similarly, and for the same reasons, it is also highly desirable to have the valve member close sharply and fully when the fluid pressure drops below a predetermined minimum fluid pressure.
Numerous attempts have heretofore been made to design valves with particular features designed to increase the sharpness with which the valve member opens and closes, as, for example, U.S. Pat. No. 3,354,900to Ferrill which discloses a valve having a huddling chamber formed with an outlet passage that is gradually reduced as the valve member beings to open and is gradually increased as the valve member closes. Moreover, in U.S. Pat. No. 3,027,912to Carr a huddling chamber is provided to assist in raising the valve member, and in U.S. Pat. No. 3,411,530to Powell a lip is located on the valve to direct exiting fluids downwardly while a restricted passageway is provided around the valve member to cause a pressure imbalance thereacross when the valve member first opens. Finally, in U.S. Pat. No. 3,757,815 to Orr, the seating surface of the valve member is formed with recesses that create turbulence in the exiting gases to thereby increase the pressure exerted against the valve member by the exiting gases when the valve member first opens.
In accordance with the present invention, a particular huddling chamber and fluid directing means are provided for simultaneously creating turbulence in the exiting fluid and initially restricting the passage of exiting fluid from the huddling chamber to cause a sharp opening and closing of the valve member.